Die for hydrostatic extrusion

ABSTRACT

A composite die for hydrostatic extrusion is composed of a preforming portion with a conical inlet portion and an endforming portion, separated from each other along a radially dividing plane. A force-absorbing support ring surrounds that part of the end-forming portion which is in contact with and nearest the pre-forming portion. There is a gap on the outside of the part of the end-forming portion remote from the pre-forming portion. Separate rings surround and abut the calibrating endforming portion and the support ring.

nited States Patent Nilsson et a1.

[451 Oct. 28, 1975 DIE FOR HYDROSTATIC EXTRUSION Inventors: Jan Nilsson,Robertsfors; Pertti Syvakari, Helsingborg, both of Sweden AllmannaSvenska Elektriska Aktiebolaget, Vasteras, Sweden Filed: Jan. 23, 1975Appl. N0.: 543,473

Assignee:

Foreign Application Priority Data Jan. 29, 1974 Sweden 74011107 U.S. Cl72/467; 72/60 Int. Cl. B21C 25/02 Field of Search 72/467, 60, 253

References Cited UNITED STATES PATENTS l/1912 Stratton et al. 72/481 X3,109,663 11/1963 Phillips, Jr. 279/41 3,191,374 6/1965 Ege 72/467 X3,691,816 9/1972 Strandell 72/467 Primary Examiner-Milton S. Mehr [57]ABSTRACT A composite die for hydrostatic extrusion is composed of apreforming portion with a conical inlet portion and an end-formingportion, separated from each other along a radially dividing plane. Aforceabsorbing support ring surrounds that part of the andformingportion which is in contact with and nearest the pre-forming portion.There is a gap on the outside of the part of the end-forming portionremote from the pre-forming portion. Separate rings surround and abutthe calibrating end-forming portion and the support ring.

5 Claims, 2 Drawing Figures Sheet 1 of 2 US. Patent 0m. 28, 1975 DIE FORHYDROSTATIC EXTRUSION BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates to a die for hydrostaticextrusion which is composed of two or more individual parts. The purposeof the invention is to reduce the stresses in and around the die openingand accordingly reduce the risk of rupture and increase the life, andalso to facilitate and reduce the cost of the manufacture of the die.The die is particularly intended for hot extrusion where the hightemperature of the billet increases the stresses in the die. Differentkinds of equipment in which the die may be used are described more fullyin, for example, US. Pat. Nos. 3,702,555 and 3,751,958.

2. The Prior Art In a press for hydrostatic extrusion, a die projectsinto a pressure chamber and rests on a die support which takes up axialforces operating outwardly on the die. Usually the die support alsoprojects somewhat into a cylinder which forms part of the pressure cham'ber. The die is surrounded by the pressure medium which acts on thebillet to be extruded. The pressure medium brings about forces actingradially inwardly on the outer surface of the die. The billet to beextruded produces outwardly acting radial forces in the inlet portion ofthe die. As far as up to the die opening these radial forces balanceeach other, but beyond the smallest calibrating cross-section of the diethe radial inner pressure ceases, so the forces produced by the pressuremedium give rise to very great stresses at the inner surface of the die.A stress factor greater than two is obtained for thick-walled tubes incase of an outer load, that is, the stresses at the inner surface aremore than twice as great as at the outer surface. The outer load itselfis great, usually from to kbar. A die manufactured in one piece has alsoa shape which is less suitable from the point of view of hardening, andmust of course have the same high-tensile material in the inlet portionas at the die opening, in spite of the fact that the material in theinlet portion is not subjected to the same high stresses. This resultsin a bad utilization of the material in the inlet portion of the die.

SUMMARY OF THE INVENTION According to the invention, the die is composedof two or more annular portions which are separated by substantiallyradial dividing lines. A first portion has a conical opening and forms apreforming portion, and a second portion having an opening which closelyfollows the first portion forms an end-forming and calibrating portion.The end-forming and calibrating portion is surrounded by a third ringand is attached in this ring in a prestressed manner. The prestressingmay vary axially so that it is lower at its outer surface than at itsinner portion. The same effect can be attained by giving the third ringa smaller axial extension than the endforming and calibrating portion,thus obtaining a suitable balancing of outwardly directed radial forces.The outer limit surface of the end-forming and calibrating portion canadvantageously be located immediately behind the smallest cross-sectionof the die opening. It may then be appropriate to form the die with athird and a fourth ring which make contact with the endforming andcalibrating portion and the surrounding prestress ring, respectively.These third and fourth rings are given such dimensions that a radial gapis formed between them. In this way the stress caused by the pressuremedium at the opening of the inner ring is reduced. The rings can bemade with different thicknesses so that a radial gap is formed betweenthe endforming ring and the ring below the prestress ring. All theannular parts mentioned are held together by a surrounding ring and bylocking rings.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described more fullywith reference to the accompanying drawing. FIGS. 1 and 2 show dies ofdifferent embodiments placed in a pressure chamber in a press of thekind described in US. Pat. No. 3,751,958.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the FIGS., 1 designates apress table in a press stand, the rest of which is not shown, and 2 ahighpressure cylinder which is part of a high-pressure chamber. In thecylinder there are a support cylinder 3 for taking up forces from a tubemandrel, a seal 4 consisting of an inner sealing ring 4a and an outersealing ring 4b, and a spacing tube 5 which holds the seal 4a, 4baxially fixed to the seal holder 6. A die support 7 rests on the presstable 1 and projects into the cylinder 2. The die support is providedwith a guide ring 8 for centering a die 9a, which rests on the diesupport 7.

In the embodiment according to FIG. 1, the die 9a consists of aplurality of annular parts. The part 10 forms a preforming portion andhas a concial opening 11. Below this there is an annular end-forming andcalibrating portion 12 with a conical opening 13 which closely conformsto the opening 11 in the preforming portion 10. Furthermore, there are asubstantially cylindrical opening 14 and, below this, a portion 15 witha somewhat larger diameter than the opening 14. The part 12 issurrouonded by a ring 16 and is attached into this ring at least alongpart of its axial extension. In the embodiment shown, the support ring16 has a smaller thickness than the end-forming portion 12, so that thering is engaged into the part of the portion 12 nearest to thepreforming portion 10 but not in its outermost part. The preformingportion 10, the end-forming and calibrating portion 12 and theattachment ring 16 are held together by a ring 17 and by locking rings18 and -19. The die support 7 is formed with support surfaces 21 and 22in different planes at the same axial spacing as the outer surfaces ofthe parts 12 and 16. Between the outer cylindrical surface of theend-forming portion 12 and the step between the surfaces 21 and 22 thereis a gap 23 so that the die support 7 can be compressed radially withoutcoming into contact with the outer cylindrical surface of theend-forming portion 12. Because the end-forming portion 12 is attachedin the support ring 16 in a prestressed manner, the billet, when it ispressed against the conical openings 11 and 13 of the die duringinsertion, is prevented from giving rise to tensile stresses in theend-forming portion 12, which stresses might cause said portion toburst. Further, the shape of the die causes the ring 16 and the pressuremedium acting thereon to operate only on that part of the end-formingportion 12 which is exposed to outwardly directed radial forces duringthe pressing, that is, substantially only on the part which is locatedoutside the conical portion 13 and the die opening portion 14. The shapeof the die also means that the pressure medium is prevented from causingdangerous compressive stresses in the clearance portion in the dieopening where there are no radially outwardly directed forces during thepressing.

In the embodiment according to FIG. 2, the die 9b contains a preformingportion 10, an end-forming portion 12 with a prestressed support ring 16and also two rings and 26. The outer end surfaces of these rings arelocated at the same plane. The ring 26 has thus a greater thickness thanthe ring 25.

The outer diameter of the ring 25 is smaller than the inner diameter ofthe ring 26, so that a radial gap 27 is formed. The ring 26 is formedwith a radially inwardly directed flange 28 which projects into a recess29 in the ring 25 in order to fix this ring axially. The parts of thedie are held together by a ring 30 and two locking rings 31 and 32.Because of the gap 27 between the ring 25 and the ring 26, the ring 26must be deformed radially under the action of the pressure medium aroundthe die before it is pressed against the ring 25. If possible, the playbetween the ring 26 and the ring 12 should be so large that said ringsdo not make contact with each other during the pressing. In this way itis possible to limit the stress caused by the pressure medium in thering 12 and in the opening in the ring 25. When a die of this design isused, the end surface 34 of the die is of course completely plane.

One further advantage of a composite die according to the invention isthat different materials can be chosen for different parts of the die.This means that a material of very high strength can be chosen in theendforming and calibrating portion of the die, and that this part can begiven improved properties more easily by heat treatment because of itsrelatively small dimensions, which results in a reduced risk ofdangerous stresses due to the heat treatment, and thus higher strength.It will also be possible to use hard metal in the die, or othermaterials which can be manufactured in the large sizes required for anundivided die only with considerable difficulty. The die will also beless sensi tive to such heat shocks which arise from contact with aheated extrusion billet. The cost of the die is also reduced by the factthat relatively inexpensive materials can be used in the main part ofthe die. In case of damage to the die, normally only the end-forming andcalibrating portion of the die needs to be replaced. Further, the sameelements can be used to a great extent for extruding products ofdifferent cross-sectional areas.

We claim:

1. Composite die for hydrostatic extrusion with a preforming portion(10) with a conical inlet portion (11) and an end-forming portion (12)separated along at least one substantially radial dividing plane, and aprestressed solid closed force-absorbing/support ring (16) surroundingand contacting the end-forming portion and supporting the end-formingportion (12) only in that part of its height nearest the pre-formingportion (10).

2. Composite die according to claim 1, in which a gap is provided aroundthe part of the end-forming portion remote from the pre-forming portion.

3. Composite die according to claim 1, in which the thickness of thesupport ring (16) is smaller than that of the end-forming portion (12).

4. Composite die according to claim 1, which comprises a fourth ring(25) and a fifth ring (26) on the outside of the fourth ring, saidfourth and fifth rings axially abutting the calibrating portion (12) andthe support ring (16), respectively.

5. Composite die according to claim 4, in which a radial gap (27) isprovided between the fourth ring (25) and the fifth ring (26).

1. Composite die for hydrostatic extrusion with a preforming portion(10) with a conical inlet portion (11) and an end-forming portion (12)separated along at least one substantially radial dividing plane, and aprestressed solid closed forceabsorbing/support ring (16) surroundingand contacting the endforming portion and supporting the end-formingportion (12) only in that part of its height nearest the pre-formingportion (10).
 2. Composite die according to claim 1, in which a gap isprovided around the part of the end-forming portion remote from thepre-forming portion.
 3. Composite die according to claim 1, in which thethickness of the support ring (16) is smaller than that of theend-forming portion (12).
 4. Composite die according to claim 1, whichcomprises a fourth ring (25) and a fifth ring (26) on the outside of thefourth ring, said fourth and fifth rings axially abutting thecalibrating portion (12) and the support ring (16), respectively. 5.Composite die according to claim 4, in which a radial gap (27) isprovided between the fourth ring (25) and the fifth ring (26).